Present warhead concepts utilize single or multiple detonators which initiate the explosive at a point. Actually, the detonators initiate the explosive over a surface, but the surface area is so small in relation to the dimensions of the warhead that it is considered a point.
The warhead designer, working with point detonators, is limited in his choice of initiation schemes due to the physical size of the detonator. To initiate a warhead along any of several lines parallel to the axis and surface of the explosive charge requires relinquishing space that is normally used for fragments and using it for the detonators. Likewise, plane wave initiation cannot be incorporated in a device due to the large number of detonators needed. There do exist means for producing line or plane detonation waves which use only one detonator and a train of explosive, but these, however, are used for experimental studies and are too bulky for use in a warhead.